PROPORTIONING OF RCC RETAINING WALL

Proportioning of reinforced concrete retaining wall elements such as stem, base slab, toe slab and heel slab is important to make the design economical.
Following are the preliminary dimensions of retaining wall:
a) Width of Base Slab:
Base slab of a retaining wall is so proportioned that the vertical soil reaction ‘R’ at the base with the front face of the stem. Following figure shows the dimensioning of retaining wall.

Let h = height of the backfill from the soffit of the base slab
B = width of the base slab
X_h = width of heel slab
X_t = width of the toe slab
C_a = coefficient of active earth pressure
For economical design, the soil pressure resultant should pass line up with the front face of the stem. Assuming the soil pressure distribution as triangular with maximum pressure at the toe and zero at the heel, the resultant vertical pressure will pass through the middle third point.
Unnikrishna Pillai and Devdas Menon of IIT Madras have developed an expression for the minimum width of the heel slab as:

Width of Base = B = 1.5X_h and X_t = B/3.
b) Thickness of Base Slab and Stem:
The preliminary thickness of base slab is given by:
Tb = 0.08h but not less than 300mm.
Thickness of stem at bottom is assumed as
t_s = t_b
The stem thickness is gradually decreased towards top to a minimum value of 150 to 200mm for economical design. The front face of the retaining wall is maintained vertical.